The present invention relates to the microgrippers, particularly to shape memory polymer gripper/release mechanisms, and more particularly to a method and apparatus for loading shape memory gripper mechanisms.
In recent years, substantial research and development has been directed to microactuators, microgrippers, etc. particularly for medical applications and capable of operating in 250-500 xcexcm diameter applications, such as the blood vessels in the human body. Recently a shape memory polymer (SMP) material has been developed wherein above a certain temperature (Tc) the material becomes soft and can be shaped by applying pressure, and cooling to a temperature below Tc, and upon reheating the material to a temperature above Tc the material returns to its original shape.
By the use of the SMP material, microgrippers have been developed for applications such as depositing material (i.e., embolic coils) in the blood vessels. Due to the capability of the SMP materials, a small SMP tube attached to a guide wire or catheter is heated, an embolic coil, for example, is inserted in the tube, and pressure is applied to the SMP material causing it to conform about the coil, whereafter the SMP material is cooled thereby freezing the SMP material in the formed shape thereby gripping the coil, and upon reheating the SMP material the material returns to its original shape thereby releasing the coil. Such SMP microgrippers are described and claimed in copending U.S. application Ser. No. 08/807,412 filed Feb. 28, 1997, entitled, xe2x80x9cMicrofabricated Therapeutic Actuatorsxe2x80x9d, and assigned to the same assignee, now U.S. Pat. No. 5,911,737 issued Jun. 15, 1999.
The present invention involved the loading of the SMP tubing with deposit material for medical applications, such as an embolic coil, medication, etc., and for non-medical applications requiring the delivery and release of components in normally inaccessible areas. The apparatus of the present invention operates via differential pressure between vacuum and hydrostatic water pressure whereby an application of uniform pressure on the exterior of the SMP tubing, with a vacuum on the interior thereof causes heated SMP tubing to change shape and grip a device located therein, after which the SMP tubing is cooled and thereby freezes in its changed shape. The heating and the cooling of the SMP tubing can be accomplished by the water utilized to produce the pressure for changing the shape of the SMP tubing. The heating of the SMP tubing may also be accomplished using optical fibers and laser light. Also, either heated water passing through a catheter to which the SMP tubing is attached or laser light via optical fibers packed to the SMP tubing may be utilized to reheat the tubing and release the device therefrom.
It is an object of the present invention to enable loading of shape memory polymer material with a deposit material.
A further object of the invention is to provide a method for loading a shape memory polymer tubing with a device to be gripped and released thereby.
A further object of the invention is to provide a loading mechanism for shape memory polymer gripper/release mechanisms.
Another object of the invention is to enable loading of a shape memory polymer gripper/release mechanism utilizing differential pressure on the external and internal areas of the shape memory polymer material.
Another object of the invention is to provide loading of a shape memory polymer tube with a device to be gripped/released thereby, utilizing differential pressure between vacuum and hydrostatic water pressure.
Another object of the invention is to provide loading of a shape memory polymer gripper/release tubing utilizing pressured water which is heated and cooled on the external area of the tubing while drawing a vacuum in the internal area thereof, and applying a mechanism to areas of the heated external area of the tubing to form depressions therein which are frozen in the tubing by cooling of the external area.
Another object of the invention is to provide loading for a shape memory polymer gripper/release tubing utilizing laser heating of the tubing and differential pressure and cooling for forming depressions in the tubing for gripping a device positioned therein.
Other objects and advantages will become apparent from the following description and accompanying drawing. The invention involves the loading of a shape memory polymer SMP gripper/release mechanism with a device to be gripped and released. The invention is carried out by inserting in an SMP tubing a device to be gripped/released, utilizing differential pressure between the internal and external areas of a SMP tubing after and/or during the heating of the tube whereby depressions are formed in the tubing, and thereafter cooled the tubing causing a freezing of the thus formed depressions in the tubing which causes gripping of the device located in the tubing. Release of the device from the SMP tubing is accomplished by reheating the tubing such that it returns to its original shape. The method and apparatus of this invention requires the use of an SMP tubing having a glass transformation temperature (Tg) which when heated above Tg can be reshaped, and subsequent cooling below Tg freezes to tubing in its reshaped configuration. The heating and/or cooling can be provided by the same water applied for pressurization, or the heating can be provided by optical fibers packaged with the SMP tubing via which laser light, for example, is directed onto the tubing. The heating and cooling may be carried out during pressurization of the tubing by controlling the temperature of the water used in the differential pressure application to the tubing.